Coaxial cables transmit radio frequency (“RF”) signals between transmitters and receivers and are used to interconnect televisions, cable boxes, DVD players, satellite receivers, modems, and other electrical devices and electronic components. Typical coaxial cables include an inner conductor surrounded by a flexible dielectric insulator, a foil layer and/or a metallic braided sheath or shield, and a flexible polyvinylchloride jacket. The RF signal is transmitted through the inner conductor. The conductive sheath provides a ground and inhibits electrical and magnetic interference with the RF signal in the inner conductor.
Coaxial cables must be fit with cable connectors to be coupled to electronic components. Connectors typically have a connector body, a threaded fitting or coupling nut mounted for rotation on an end of the connector body, a bore extending into the connector body from an opposed end to receive the coaxial cable, and an inner post within the bore coupled in electrical communication with the fitting. Generally, connectors are crimped onto a prepared end of a coaxial cable to secure the connector to the coaxial cable. The connectors must maintain electrical connection and signal shielding with the cable despite rotation, tugging, bending, or other movement of the cable and the connector. Movement of the cable and the connector may occur suddenly if an object contacts the cable or connector, but may also occur slowly over time, such as from cyclical heating and cooling or wind loads on outside installations.
Some approaches to maintaining continuity have focused on maintaining a connection between the coupling nut and the post by biasing the nut in an axial direction so as to force the nut into continuity. This has generally been accomplished by loading the nut axially with a spacer, washer, or other shimming device. Typically, such biasing devices are disposed axially between the nut and the body of the connector and urge the nut axially forward into contact with a forward flange on the post. However, should the biasing device not provide an even force continuously around the entire device, the nut may not mate continuously flush against the post, which can lead to leaks in signal, degradation of continuity, and impingement of RF interference into the connector. Further, if the connector is bent, such as frequently occurs when the cable extending from the connector flexes or is bent, the nut will not mate continuously flush against the post, leading to the above-stated problems.
Other biasing devices have been used to shim the nut against the post. Such devices are typically disposed annularly between the nut and the post and have a ramped or wedge-like profile. When the nut is tightened onto the mating port of an electronic component, the biasing device is compressed and exerts an axial bias along its ramp against the nut, thereby causing the nut to move forwardly into contact with the forward flange on the post so as to establish continuity. U.S. Pat. No. 8,517,763 describes an integrally conductive locking coaxial connector that relies on such operation for continuity: a rear flange of the nut has an inclined inner surface that roughly corresponds to a ramped outer surface of a washer disposed between the nut and the post which the washer surrounds. When the nut is not applied to the mating port, the washer is loose in a space between the nut and post: it can wobble and lose contact and be free of either the nut or the post. Thus, when the nut is not applied to the mating port, electrical continuity between the nut and the port is not established and maintained. When the nut is applied to the mating port but not tightened, the same problem exists: the washer is loose and does not maintain continuity between the nut and the mating port. The connector in the '763 patent requires the coupling nut to be tightened on the mating port; when the nut is threadably engaged and tightened onto a mating port, the nut advances forward on the post and its inclined inner surface encounters the ramped outer surface of the washer, thereby forcing the washer forward as well, into confrontation with a forward flange of the post and against which the washer is axially compressed. This axial compression of the washer between the post and the nut maintains electrical continuity in an axial direction through the connector.
Other connectors rely on compression in a similar fashion. For instance, U.S. Pat. No. 9,343,855 discloses a spring-like washer element disposed between the post and the coupling nut mounted on the post. The washer element there includes a number of obliquely-projecting flexible fingers. These fingers roughly correspond to an inner chamfer or inclined surface of a rear flange on the coupling nut. An annular base portion of the washer element encircles the post, and the fingers project radially outward and axially forward from that base portion. When the connector is free of the mating port, the washer element is loose and does not maintain continuity between the coupling nut and the post. Likewise, the washer element is still loose when the connector is applied to the mating port but not tightened. Only when the connector is tightened is continuity established. As with the connector of the '763 patent, continuity through tightness requires the washer to be compressed. In the case of the '763 patent, the washer is compressed both axially and radially by the inclined surface of the rear flange on the coupling nut. This causes the washer to lock the coupling nut with respect to the post and body of the connector.
The connectors of the '763 and '855 patents exemplify the problem experienced by connectors that rely on compressing a washer in order to maintain continuity: they bind, seize up, are difficult to use, and are vulnerable to exterior forces backing the connector of mating port. When the connector binds, it becomes increasingly difficult or impossible to turn, which makes installation difficult: many technicians rely on the feel of increased rotational resistance when applying a connector to the post of an electronic component to determine when the connector is fully seated on the mating port. This “feel” leverages what is known as high free nut torque: essentially, the torque required to rotate the nut on the connector even before the nut is mated and seated to the mating port. When free nut torque is low, the nut is easy to rotate and it is very easy to tell when the nut is properly seated and mated with mating port of the electronic component: the torque required to turn the nut suddenly and dramatically increases. When free nut torque is high, the nut is difficult to rotate and it becomes difficult for an installer to determine whether the connector is properly seated with a mating port because the torque required to rotate the coupling nut increases by a relatively minor amount, but yet still binds. Most conventional continuity connectors have very high free nut torque.
When the nut binds prematurely because of the axial forces imparted by a shim or other biasing device, the technician can be fooled into thinking that the connector is properly installed on the mating port, when it may only be partially installed. This is a lack of continuity which leads to a degradation of signal quality. Further, should the nut be cross-threaded or not be evenly applied on the threads of the post of the electronic component, the coupling nut may not mate continuously flush against the mating port, which can further lead to leaks in signal, degradation of continuity, and impingement of RF interference into the connector. And again, if the connector is bent, the nut will not mate continuously flush against the mating port, leading to the above-stated problems. The reliance of such connectors on the existence and exertion of compression and/or axial forces to establish continuity is at best undesirable and at worst impractical and forces a corresponding dependence on perfect and precise design dimensioning and manufacturing dimensional tolerances, perfect assembly, and proper installation and operation, which is rarely possible in the real world. A connector that provides improved connectivity and continuity is needed.